1. Technical Field
The present invention relates to a communication network using an asynchronous transfer mode ATM and particularly to a traffic control method and system for controlling traffic flow of a stream of cells in a broadband user-network interface in an ATM communication network.
2. Background Art
Generally, reference configuration of a user-network interface of a broadband-integrated service digital network B-ISDN is prescribed by CCITT Recommendation I.413, an international standard used to describe physical layer information flows according to the broadband-integrated service digital network B-ISDN protocol and identifies interface functions. CCITT Recommendation I.4:13 also sets standards for respective functional groups and reference points to be adapted for the characteristics of the B-ISDN on the basis of a reference model of an existent narrow band-integrated service digital network N-ISDN.
FIG. 1 illustrates a typical physical configuration of a user-network interface of the broadband-integrated service digital network B-ISDN as recommended by the CCITT based on the reference model of an N-ISDN. In this configuration, the user-network inface includes essential functional groups such as a broadband-terminal equipment B-TE 10, a broadband-network termination B-NT2 12, a broadband-network termination B-NT1 14 and a local exchange LEX 16. Additional terminal equipment TE (not shown)and broadband-terminal adaptor B-TA may be connected to the B-NT2 12 for providing a matching or adaptation function. Reference points S.sub.B and T.sub.B for channel interface structure and distinguishing the respective functional groups are also established.
Referring to FIG. 1, the B-TE 10 is referred to as all purpose communication equipments with broadband communication functions such as telephones, facsimile machines, televisions, computers, etc., and is also referred to as a multimedia terminal with more advanced functions. Typical functions of the B-TE 10 are upper level protocal handling, maintenance, interface functions and connection services. The B-NT1 14, on the other hand, supplies functions that are broadly equivalent to those of a physical layer of an open system interconnection OSI model. Examples of B-NT1 14 functions are transmission interface handling, maintenance, and modulating/demodulating for physical transmission and reception of data via the physical layer.
Similarly, the B-NT2 12 contains functions found in the physical layer with additional functions found in upper layers of the OSI model. The main functions of the B-NT2 12 are however, a connection admission control CAC, generic flow control GFC, multiplexing and demultiplexing, resource management, signaling, usage parameter control UPC, and switching function among internal terminals. These are most essential functions in the user-network interface (hereinafter referred to as `UNI`).
The B-TA connected between the TE and B-NT2 12 (not shown) is a protocal convertor that serves as an intermediation for matching existent simple, slow, and low functional terminals having no broadband function with high function terminals having broadband functions, for converting signals of different protocol with one another.
The LEX 16 performs a switching function through the B-ISDN to a destination node. Although the LEX 16 is not a component of the UNI, it controls usage parameters of the traffic of an incoming stream of cells into a network from the interface, and notifies possible congestions occurring in the network for performing necessary operation and maintenance OAM function of the UNI. As shown in FIG. 1, a construction L by layers of the functional groups exists in the UNI(H). A physical layer PHY serves to receive or transmit direct electrical signals in media using broadband communication; and an synchronous transfer mode ATM layer executes all traffic control functions for controlling a cell as an information transmission unit input through the physical layer PHY. An ATM adaptation layer AAL supports higher-layer functions of the subscriber and control planes and supports connections between ATM and non-ATM interfaces. Information is mapped by the adaptation layer into cells. At the transmitting end, information units are segmented or are collected to be inserted into ATM cells. At the receiving end, the information units are reassembled or read-out from ATM cells. A stream of ATM cells by layers is shown in FIG. 1 by an arrow having an up stream direction toward a network.
Typically, in the construction of FIG. 1, the connection admission control CAC of the B-NT2 12 determines all controls which are performed by the network during a call establishment. For instance, when a subscriber makes a call establishment request, the CAC analyzes the request and determines whether a connection thereto is admitted in accordance with the network state. The CAC then assigns necessary resources such as bandwidth, buffer capacity, etc., and assigns a virtual path identifier VPI and virtual channel identifier VCI in order to execute a path set function to destination. When issuing a call connection request, the subscriber suggests a source traffic descriptor comprised of traffic parameters defining various traffic characteristics and quality of services QOSs that are required for a call. The CAC must not have any effect on other subscribers who are admitted. It is also possible that the subscriber who has already admitted in making a connection to require improved services by simply re-negotiating with the network, if necessary.
The generic flow control function GEC serves to adjust a traffic flow between the B-TE 10 and B-NT2 12. That is, the most important control object of the generic flow control GFC function is to guarantee fairness of traffic toward the network and to minimize transmission delay of the delay sensitive traffic.
The usage parameter control UPC monitors whether a connection-admitted call observes previously negotiated traffic parameters; that is, whether a stream of cells representative of a call violates the previously required traffic parameters in order to prevent congestion in the network. In general, the UPC has two functions. The first function is to monitor whether some parameters describing the traffic characteristics of the cells are observed. Various algorithms have been proposed for the UPC in accordance with a monitoring method of a bucket type or a window type. The second function is to control a cell loss priority CLP bit so as to keep a cell lost ratio low. Then, after the CLP bit is set to 1 by a tag function, and if congestion occurs within the network, all tagged cells are eliminated, or otherwise, are stored into a temporary buffer for subsequent shaping function. Performance of the usage parameter control UPC algorithm is measured as follows: First, whether a function part is excellent in searching an erroneous traffic state. Second, whether a monitoring time interval is selected. Third, how fast is the response speed. Finally, how easily can the UPC algorithm be implemented. However, the UPC should also consider whether the quality of service QOS having direct influence on the traffic of the subscriber is guaranteed and resource is varied in accordance with circumstances.
Typical algorithms of the usage parameter control UPC are leaky bucket, jumping window, and moving window types. In addition to these, there are various algorithms which are made by modifying existing methods such as shaping, varying window time, etc.
The source traffic descriptor and quality of service QOS are suitably defined for the connection admission control CAC and using parameter control UPC. The source traffic descriptor contains source traffic parameters with traffic characteristics that are descriptive of the ATM cells. Source traffic typically uses an ON-OFF traffic in which an ON state enables a continuous generation of ATM cells and an OFF state disables the generation of ATM cells. A stepwise variable traffic in which a cell rate is a time variable and a constant bit rate traffic in which the cell rate remains unchanged may also be used.
Source traffic parameters described by the source traffic descriptor are, for example, a maximum cell rate, average cell rate, burstiness cell rate, and mean cell duration. Further, the quality of services QOSs are a cell loss ratio, cell delay, and cell delay variation may also be included. In order to satisfy a grade of service GOS and the QOS, the resource management RM function serves to assign resources necessary to execute transmission function, switching function, and control function. A necessary resource for this end is provided with a transmission bandwidth and a buffer capacity according to a transmission capacity. The function for assigning a resource is largely divided into two functions; first, when a call is established, a bandwidth is assigned by the CAC function and second, after a call is already connected, a bandwidth assignment request occurring during service, i.e., a bandwidth request occurring by the UPC function is managed within real time.
To easily and simply execute the resource management RM function as well as correct control function for transmitted traffic, there is a method of controlling the traffic by setting a virtual path VP. In this method, when performing the CAC, admission is determined at the end terminal of a virtual path connection VPC. At this time, great speedy and case control are possible in a transmission node of traffic without requiring a control process such as the VPC. Since a switching node stores a reference table for a virtual path identifier VPI, by updating the reference table, rapid re-establishment of path is possible in the switching node. A plurality of virtual channels VC are processed in the bundle form to control a small number of the virtual path VP, thereby resulting in simplifying the overall control function. As a result, architecture of the whole network can be made to be simplified.
In the meantime, in the resource management RM, the method of assigning bandwidth is divided into peak rate assignment and statistical assignment. The peak rate assignment does not have statistical multiplexing gain, and its utilization is very low. One of typical features of the ATM transmission method is the statistical multiplexing gain. A main concern in the method is in that the quality which calls during service are not damaged with assignment of possible least bandwidth.
The UNI function constituted as FIG. 1 has an interfacing function, so that a subscriber can connect the B-ISDN and can receive a necessary service. Further, the UNI(H) shown in FIG. 1 should meet with service required by the B-TE 10 in which call connection is admitted. Main functions of UNI(H) in FIG. 1 is to distribute a proper resource to call establishment request of a subscriber, to assign the virtual path identifier VPI/virtual channel identifier VCI, to control properly the traffic in order to previously prevent congestion within the network or to recover already occurred congestion, and to maximize efficiency of a given resource to operate the whole network in an optimum state. Further, the UNI(H) is necessary to ensure the variety and flexibility for a multi media service.
However, in spite of many advantages of the ATM, development of this field has been hindered due to difficulty of correct control and complexity of implementation thereof, in case that a number of subscribers require various kinds of services.